As methods for constructing pavements of roads, port facilities, airport runways, and the like, methods utilizing a PC pavement and a RC pavement are known. The PC pavement is a pavement in which a prestressed concrete (PC) pavement boards are disposed on a roadbed and a backfilling grout material is injected into a gap between the PC pavement hoards and the roadbed. The RC pavement is a pavement in which a reinforced concrete (RC) pavement board is used in place of the PC pavement board.
Further, as a pavement for heavy traffic roads, a semi-flexible pavement is known. The semi-flexible pavement is a pavement in which cement milk is injected into an open-graded asphalt mixture having a large porosity.
An injection grout for pavement, which is used as a raw material for a hack-filling grout material used for the PC pavement and the RC pavement, cement milk used for the semi-flexible pavement, and the like, is a composition containing cement. The cement composition to be used as the injection grout for pavement is usually a rapid-hardening cement composition in which a rapid-hardening admixture is contained to harden the cement at an early stage so that work is done at night and a road is opened to traffic next morning.
As the rapid-hardening admixture of the rapid-hardening cement composition, an admixture in which calcium aluminate and inorganic sulfate are combined (blended) is known. However, there have been problems that this rapid-hardening admixture in which calcium aluminate and inorganic sulfate are combined has a strong action of accelerating hardening of the cement, and, in the cement composition containing this rapid-hardening admixture, a time (setting initial time) from addition of water until the cement starts to set is short so that sufficient pot life cannot be secured. For this reason, in an admixture in which calcium aluminate and inorganic sulfate are combined, a setting modifier is added so as to regulate (control) the setting initial time of the cement composition. As the setting modifier, inorganic carbonate, oxycarboxylic acid, or sodium aluminate is used.
Patent Document 1 discloses an ultra-rapid-hardening cement composition which contains a quick-hardening cement as a main component, and the quick-hardening cement contains 15 to 35% by weight of a quick-hardening component in which a weight ratio of calcium aluminate:inorganic sulfate is 1:0.5 to 1:3, and the ultra-rapid-hardening cement composition contains, in terms of internal proportion of weight, 0.2 to 3% of sodium aluminate, 0.2 to 5% of inorganic carbonate, and 0.1 to 2% of oxycarboxylic acids.
Patent Document 2 discloses an injection grout for pavement which contains a rapid-hardening admixture, a cement mineral, sand, and a powdered emulsion. This Patent Document 2 discloses that sodium aluminate, inorganic carbonate, and carboxylic acids are used as setting modifiers of the rapid-hardening admixture, and these setting modifiers have a particle size constitution including 10 to 45% by mass of first particles having an average particle diameter of greater than 45 μm and equal to or less than 90 μm, 30 to 70% by mass of second particles having an average particle diameter of greater than 90 μm and equal to or less than 150 μm, and 5 to 30% by mass of third particles having an average particle diameter of greater than 150 μm and equal to or less than 500 μm, in which the second particles are included in an amount which is larger than the amount of the first particles and also larger than the amount of the third particles.
It is required that a rapid-hardening cement composition containing a rapid-hardening admixture can stably and sufficiently secure a pot life, that is, a setting initial time is stable and long, and fluidity is high during a period from addition of water until hardening reaction proceeds. In addition, after completion of construction work, it is required that hardening occurs at an early stage and high strength (compression strength) is developed, that is, excellent properties of early age strength are exhibited.
However, in the ultra-rapid-hardening cement composition disclosed in Patent Document 1, there have been problems that it is difficult to secure a long pot life as long as 60 minutes without reducing the compression strength at an early age (about 3 hours of age), and spots are observed on a hardened body of the cement composition and these parts become defects, and thereby causing a decrease in long-term strength. In addition, there was a problem in that the setting time greatly varies depending on an environmental temperature, and thereby resulting in poor workability at a construction site.
Further, in the injection grout for pavement disclosed in Patent Document 2, by specifying the particle size constitution of the setting modifiers contained in the rapid-hardening admixture, the properties of early age strength and the environmental temperature dependent properties of the setting time are improved. However, in the case where the injection grout for pavement disclosed in Patent Document 2 in which the rapid-hardening admixture is mixed is stored for about 3 months, the setting time may be greatly changed as compared with the setting time immediately after production and the properties of early age strength may be decreased.